Semiconductor Device I-V Measurement System
Semiconductor Device I-V Measurement System
for Temperature and Magnetic Field Characterization
Introduction:
This document describes the operation of the instrumentation system shown in the schematic of Figure 1. The hardware for this system resides in the Device Measurement Lab of the USM Electrical Engineering Department. Software has been written in LabView G code which combines the operation of the individual instruments into a single device characterization system. The program written to do this is named “Combined control.vi”. Several other programs have been written which make possible the operation of individual instruments. Individual operation of instruments can have many applications including system debugging should problems arise.
Figure 1: System Schematic
Description:
The program “Combined control.vi” together with the hardware makes possible the simultaneous acquisition of test data such as temperature, applied magnetic field, and semiconductor parametrics. The program then allows for the saving of acquired test data to a comma delimitered spreadsheet file.
A list of the hardware utilized for the test system is given below.
Equipment List
1.Pentium PC running Windows 95, installed with a National Instruments AT-GPIB/TnT card, and LabView 4.0 software.
2.two Keithley 236 Source Measure Units (SMUs).
3.one Keithley 213 Quad Voltage Source.
4.one Oxford Instruments ITC4 Temperature Controller.
5.one Magnion Electromagnet and Magnion Precision Magnet Power Supply.
6.one Group-3 141D Digital Tesla Meter and measurement probe.
7.one low temperature environment, test fixture.
8.four GPIB cables.
9.one serial (RS232) cable.
At the time this document was written item 7, the low temperature fixture, has yet to be assembled. Also, at the time of this writing item 4, the Oxford ITC4 Temperature Controller, needs further setup work in order to improve the accuracy of its temperature measurements.
The addresses of the GPIB instruments have been pre-set for compatibility with the software that has been written. A list of the GPIB instruments and their addresses is given below.
GPIB Addresses
1.Pentium PC (via AT-GPIB/TnT card): GPIB address 0.
2.first Keithley 236 SMU: GPIB address 16.
3.second Keithley 236 SMU: GPIB address 17.
4.Keithley 213 Quad Voltage Source: GPIB address 9.
5.Group-3 141D Digital Tesla Meter: GPIB address 1.
The Oxford Instruments, ITC4 Temperature Controller is the only instrument not communicating with the PC by GPIB. The ITC4 uses RS232 serial protocol.
The Oxford ITC4, RS232 Communication Setup
1.Serial port 1
2.Com 2
3.Eight data bits
4.One stop bit
5.No parity bits
It is important to note that the electromagnet is controlled by an analog voltage signal which is output from the Keithley 213 Quad Voltage Source. That is, the magnetic field is not directly controlled with GPIB or RS232 commands but is instead controlled through an intermediary GPIB device by specifying an analog voltage.
Operation of “Combined control.vi”
“Combined control.vi” can be opened by clicking on the shortcut icon appearing on the front panel of Windows.
After opening the program, start the programby clicking the cursor on the arrow shaped run button in the tool bar. When the program is running, the run button will have a faded. dashed appearance indicating operation. A series of option screens will then be presented requiring user input.
It is important that all GPIB instruments connected to the GPIB bus be turned on. Even instruments that will not be used in a data acquisition session must be powered up. Unpowered instruments on the GPIB bus will attenuate the signal of the powered instruments raising the potential for data errors.
There are three ways to stop the program once it has started. The first and preferred method is to use the software quit commands provided on most screens. The second method is to use the red, “Stop Sign” shaped, stop button in the Labview tool bar. Sometimes the program will have to be paused before the stop button will work: the pause button is located in the Labview toolbar and has as a symbol two vertical, parallel lines. If the program has been paused and then stopped, the pause button will turn yellow: the pause button will have to be deactivated by clicking or the program will not run correctly when restarted. The third and least preferred method to stop “Combined control.vi” is to simultaneously press the Ctrl, Alt, and Delete buttons on the keyboard. Windows will then ask you if you want to stop the program. The third method is to be used only if the first two methods fail to respond.
The first screen presented by “Combined control.vi” is shown in figure 2. This screen gives the user the option of not including temperature control or magnet control (SMU measurements would be done at room temperature and the magnet would apply no field).
If the decision was made to include temperature control, the second screen is titled “Input Temperature Sweep Parameters”. The second screen is shown in figure 3. A temperature sweep is completely specified by a “Start Temperature”, the “Number of Steps”, and a “Step”. “Step” can be negative as well as positive. A “Number of Steps” of zero is entered if only a single temperature point is desired.
If the decision was made to include magnetic field control, the third screen is titled “Magnet Control Voltage: Input Sweep Parameters” (see figure 4). It is important to note that the user specifies control voltage values and not magnetic field. A magnetic field sweep is completely specified by a “Start Voltage”, the “Number of Steps”, and a “Step”. A “Final Voltage Level” is then calculated. “Step” can be negative as well as positive. A “Number of Steps” of zero is entered if a single field point is desired. “Start Voltage”, “Step”, and “Final Voltage Level” must be between 0 volts and 10 volts. The program automatically corrects the user if data is entered outside the 0 volt to 10 volt range.
Thefourth screen presents the user with the choice of either doing a single SMU, two terminal sweep or a two SMU, Family of Curves sweep (see figure 5).
Figure 2: First Screen of “Combined control.vi”
Figure 3: Second Screen of “Combined control.vi”
Figure 4: Third Screen of “Combined control.vi”
Figure 5: Fourth Screen of “Combined control.vi”
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